<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <style>
        #counter{
            width: 75px;
            margin: 0 auto;
        }
    </style>
    <title>Document</title>
</head>
<body>
    <div id="app">
        <div id="counter">
            <button @click="sub">-</button>
            <span>{{ num }}</span>
            <button @click="add">+</button>
        </div>
    </div>

    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    <script>
        var app = new Vue({
            el: "#app",
            
            data: {
                num: 1,
            },

            methods:{
                add: function(){
                    if(this.num === 10)
                        return;
                    this.num++;
                },

                sub: function(){
                    if(this.num == 0)
                        return;
                    this.num--
                },
            }
        })
    </script>
</body>
</html>